This practice in French has been abandoned in all good typography. No one
who subscribes to this list should perpetuate it, and that means arguing
with your customers too. Removing the accents removes vital information
from the text.
In French or in Spanish the only reason this practice arose was because
early computers were too stupid to allow access to complete character sets.
In Greek in all caps it is usual nowadays to omit the breathings and
accents. This is because now they appear as spacing characters in front of
the letter they belong to. It has not always been so, however; I have a
lovely book showing 16th-18th century Greek title pages &c. where the
diacritics are placed above the letter.
Deleted diacritics should, in general, be considered a spelling error.